One of the best places I have ever cruised actually. I take it you haven't? There are 4 big marinas in Phuket, a couple in Krabi, several yacht specialising shipyards, including in Bangkok, many international companies in the marine industry with offices in Phuket and Ocean Marina, Jomtien and smack bang on the route from the Med to the rest of SE Asia, Australia, New Zealand, etc. Hundreds of superyachts base themselves in Thai waters already. Not so much in the Gulf but Samui etc and the northern islands have a lot of traffic.